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Heat Pump vs Gas Boiler Calculator UK

Compare the running cost, 15-year total cost of ownership, and CO₂ impact of an air-source heat pump versus keeping a gas boiler. Uses the current Ofgem price cap and the UK Boiler Upgrade Scheme grant.

Interactive heat pump vs gas boiler calculator

Worked example

A typical 3-bedroom UK semi with average insulation, using the current Ofgem default tariff (electricity ≈ 27.03p/kWh, gas ≈ 6.04p/kWh), a £7,500 Boiler Upgrade Scheme grant, and a SCOP of 3.3:

Based on Ofgem price cap effective 1 April 2026.

Heat demand 13000 kWh/yr
Gas annual cost £1038
Heat pump annual cost £1287
Annual saving £-249
Heat pump net install (after BUS grant) £3500
Break-even year 19.6 yrs
15-yr net benefit vs gas £-1834

Frequently asked questions

What is SCOP and why does it matter?
SCOP — Seasonal Coefficient of Performance — is the ratio of heat delivered to electricity used, averaged over a UK heating season. A SCOP of 3.3 means you get 3.3 kWh of heat for every 1 kWh of electricity. A well-insulated home with a correctly-sized heat pump typically achieves 3.5–4.0; a poorly-insulated home or an undersized system can drop below 3.0.
How big is the Boiler Upgrade Scheme grant?
The UK government's Boiler Upgrade Scheme (BUS) offers £7,500 off the cost of an air-source heat pump for homes in England and Wales, paid directly to your MCS-certified installer. The grant is deducted from the quoted price — you never handle the money yourself.
How accurate is the running-cost estimate?
The calculation is based on the Ofgem default-tariff price cap and a SCOP derived from your insulation level. Real bills typically land within ±15% of the estimate. On a time-of-use tariff designed for heat pumps (e.g. Octopus Cosy), the heat pump running cost can be 20–30% lower than shown.
When is a heat pump NOT cheaper than a gas boiler?
At current Ofgem prices (electricity ≈ 27p/kWh, gas ≈ 6p/kWh), a heat pump needs a SCOP of roughly 4.5 just to break even on per-unit energy cost. Most homes with average insulation achieve a SCOP of 3.0–3.5. A heat pump often loses on annual running cost alone, but wins on the 15-year total cost — because the £3,500 gas-boiler replacement every 15 years and the BUS grant tip the balance. In a poorly-insulated home with no grant, the gas boiler stays ahead.

How this calculator works

The Heat Pump vs Gas Boiler calculator compares the running cost and 15-year total cost of ownership of an air-source heat pump against keeping your existing (or replacing a dying) gas boiler. The running-cost side is straightforward arithmetic: your heat demand in kWh per year, divided by SCOP for the heat pump path, multiplied by the current Ofgem cap electricity unit rate, plus standing charges — versus the same heat demand divided by boiler efficiency (we assume 90% for a condensing boiler that is properly commissioned), multiplied by the gas unit rate, plus gas standing charges. The 15-year view then adds install cost, applies electricity and gas inflation, and nets off the £7,500 Boiler Upgrade Scheme grant on the heat pump side.

Heat demand itself comes from one of two paths. If you know your annual gas use in kWh (look at the last 12 months on your bill), we use that directly and assume ~90% of it turns into useful space and water heat. If you don't, we use an archetype table indexed on property type, bedrooms and insulation level — built from MCS typical heat-loss figures and cross-checked against DESNZ housing-stock averages. SCOP — Seasonal Coefficient of Performance — is the single most important variable on the heat pump side; we default it from your insulation level (3.0 for poor, 3.3 for average, 3.8 for good) in line with the typical range reported by the MCS installer database.

Common pitfalls and things people get wrong

  • SCOP is not COP. Manufacturers quote COP (Coefficient of Performance) at a single mild test point — often 4.5 at 7°C outdoor, 35°C flow. SCOP is the weighted-average performance across a real UK heating season, and is typically 20–30% lower. A heat pump sold as "COP 4.5" usually delivers SCOP 3.2–3.5 in an average UK home. Ask your installer for the MCS-calculated SCOP for your property, not the nameplate COP.
  • Radiator sizing. Heat pumps run most efficiently at low flow temperatures (35–45°C). Existing radiators sized for a 70°C gas boiler are often undersized for that flow temperature, which forces the pump to run hotter and drops SCOP. A decent installer will model every room; a bad one will quote without looking. Budget £1,500–£3,000 for radiator upgrades on a typical 3-bed semi if your existing system was sized tight.
  • Poorly-insulated homes. A heat pump in a leaky, single-glazed Victorian terrace with SCOP 2.6 can cost more to run than the gas boiler it replaces. Insulation first, heat pump second — the BUS grant rules actually encode this, requiring your EPC insulation recommendations to be cleared.
  • Planning and noise. Since 2024 most UK heat pump installations are permitted development under relaxed rules (1 metre from boundary, below the noise threshold). Listed buildings and some conservation areas still need planning consent. Modern units run at 40–45 dB at 1 metre — quieter than a fridge — but do check your boundary distance.
  • Time-of-use tariffs change the answer. A tariff like Octopus Cosy gives you cheap electricity in three windows that align with heat-pump heating schedules; it can cut running cost 20–30% below the flat Ofgem cap this calculator assumes. If you are committed to a heat pump, factor that in rather than judging on the cap alone.

UK-specific context

The UK is an outlier among wealthy countries in how cheap gas is relative to electricity. The electricity-to-gas unit-rate ratio sits near 4.5:1 on the Ofgem cap, which is why SCOP has to be around 4.5 for energy-parity on running cost alone. The policy lever here is the "spark gap": successive governments have talked about rebalancing levies off electricity and onto gas, which would tip the running-cost maths firmly in favour of heat pumps. In the meantime, the 15-year total-cost view — boiler replacement every 15 years, £7,500 BUS grant, longer heat-pump lifespan — is what makes the economics work today for most homes that aren't uninsulated.

On carbon: UK grid electricity in 2026 averages around 180 gCO₂/kWh and is falling about 8% per year; natural gas is 203 gCO₂/kWh at the meter and does not change. A SCOP-3.3 heat pump therefore emits about one-third of the CO₂ of the gas boiler it replaces — today — and that gap widens every year as the grid decarbonises. The running-cost table in this calculator does not show CO₂ directly, but it is the biggest reason to install even when the pound-notes case is tight.

When this isn't the right answer

Don't use this calculator to decide for a flat without outdoor wall or balcony space for an outdoor unit — that's a hybrid or district-heat conversation. Don't use it if your gas boiler is under 5 years old and working well; payback restarts from zero on a new install. And if your property is truly uninsulated (no loft, no cavity, single glazing), the honest answer is insulate first — a heat pump into that house has a SCOP around 2.5 and will disappoint. This calculator models a reasonable, improvable UK home; it doesn't model edge cases.

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